1. Field of the Invention
This invention relates to a process for making polymers, and, more particularly, to a polymerization process using a mixture of free-flowing PVP-H.sub.2 O.sub.2 powder and a transition metal ion as the free radical initiator.
2. Description of the Prior Art
Free radical initiators used in polymerization processes at elevated temperatures have included alkyl peresters, dialkyl peroxides, perketals, peroxydicarbonates, hydroperoxides, peroxides, azo compounds and carbon-carbon labile compounds. Copolymerization also has been carried out at relatively low temperatures, e.g. room temperature, using a redox catalyst, such as, a combination of a redox catalyst and ascorbic acid, or, of a peroxydicarbonate and benzoin. It has been possible also to employ the polymerization initiator conjointly with a suitable accelerator, for example, an amine derived from a cyclic or phenyl structure, the amine being used by itself or together with an organic compound of a transition metal. Copolymerization also has been carried out with a mixture of different polymerization initiators having different decomposition temperatures.
The following compounds have been employed in free radical initiated polymerizations: acetyl cyclohexanesulfonyl peroxide, diacetyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, tert-butyl per [oxy]-neodecanoate, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile); tert-butylperoxy pivalate, dioctanoyl peroxide, dilauroyl peroxide, 2,2'-azobis-(2,4-dimethylvaleronitrile), tert-butylazo-2-cyanobutane; dibenzoyl peroxide, tert-butyl per [oxy]-2-ethylhexanoate, tert-butyl per[oxy]maleate, 2,2-azobis(isobutyronitrile); bis(tert-butylperoxy)cyclohexane, tert-butylperoxyisopropyl carbonate, tert-butyl per [oxy]acetate; 2,2-bis(tert-butylperoxy)butane, dicumyl peroxide, di-tert-amyl peroxide, di-tert-butyl peroxide, pinane hydroperoxide, cumene hydroperoxide, and tert-butyl hydroperoxide; and t-butylperoxy pivalate and t-amylperoxy pivalate.
These polymerization initiators suitably are used in an amount of about 0.05 to 10% by weight of the monomer or monomers, and, preferably, about 0.1 to 5% by weight of the initiator is required.
A mixture of hydrogen peroxide and a metallic ion has been used previously as a free radical polymerization initiator in several polymerizations. However, this combination can be used in aqueous systems only.
Many polymerization processes require the presence of a protective colloid in the reaction system in order to prevent agglomeration of monomer during the process. However, such protective colloids often introduce a detrimental ingredient into the polymerization mixture, which is undesirable.
Shiraeff, in U.S. Pat. Nos. 3,376,110 and 3,480,557, reacted excess hydrogen peroxide and PVP in an aqueous solution of the components. The process involved mixing PVP and a large excess of aqueous H.sub.2 O.sub.2, and evaporating the solution to dryness. Shiraeff stated that water could be tolerated in the product if it did not affect the solid dry characteristics of the complexes. The H.sub.2 O.sub.2 content of the composition was given as being at least 2%, and preferably 4.5 to 70% by weight. Prolonged drying of the composition in an attempt to reduce the water content, however, resulted in considerable loss of H.sub.2 O.sub.2. The product formed hard brittle, transparent, gummy, amorphous product of non-reproducible consistency; i.e. a variable H.sub.2 O.sub.2 content ranging from about 3.20 to 18.07% by weight, depending upon the drying times; and a considerable amount of water.
The Shiraeff PVP--H.sub.2 O.sub.2 material did not attain commercial success for any disclosed use because the product (1) was not a free-flowing powder; (2) its water and peroxide content varied widely; (3) it did not provide a consistent and reproducible product; and (4) the aqueous laboratory process could not be scaled up due to loss of H.sub.2 O.sub.2 during drying.
Merianos, in U.S. Pat. Nos. 5,008,106 and 5,066,481, described processes for making stable, high purity, free-flowing, fine white powders of substantially anhydrous complexes of PVP and H.sub.2 O.sub.2, in a defined molar ratio of constituents, e.g. 1:1, by reacting PVP and a solution of H.sub.2 O.sub.2.
Biss, in U.S. Pat. No. 5,077,047 described another process for making the Merianos product in which a fluidized bed of PVP was contacted with an aqueous H.sub.2 O.sub.2 solution. Both the Merianos and Biss methods provided free-flowing powders of PVP--H.sub.2 O.sub.2 suitable for use herein.
Accordingly, it is an object of this invention to provide polymerization processes using a free radical polymerization initiator which is a mixture of a stable, high purity, free-flowing, fine white powder of a substantially anhydrous complex of PVP and H.sub.2 O.sub.2 in a molar ratio of about 1:1, respectively, and a metallic ion, such as a transition metal ion.
A more particular object is to provide a process for polymerization of vinyl monomers such as vinylpyrrolidone.
A specific object herein is to provide polymerization processes wherein the free radical initiator can function in both aqueous and non-aqueous medium while supplying a protective colloid in situ to the polymerization system.
These and other objects and features of the invention will be made apparent from the following more detailed description of the invention.